1. Field of the Invention
This invention concerns the production of lubricating oils and greases which have superior oxidative stability.
2. Description of the Prior Art
It is known that lubricating oils tend to deteriorate after being in use for some period of time. Exposure to air, contamination by water, and contact with metal surfaces in their functional environments contribute to this deterioration. Oxidation by air is probably a most important factor contributing to degradation. As an example, in modern internal combustion engines and in turbojet engines, hot lubricants of inadequate oxidation resistance can be attacked by oxygen or air to form heavy viscous sludges, varnish and resins which become deposited on the engine surfaces. Corrosive acids also can form in this process. As a result, the lubricant cannot perform its required task effectively, and the engine does not operate efficiently. Furthermore, the sludges produced tend to foul and plug low tolerance hydraulic system components and interconnecting piping and valves.
When lubricating oils of inadequate oxidation stability are formulated into greases, similar results are encountered, thus clearly indicating the necessity for improved methods of treatment which increase the oxidative stability of lubricating oils.
Accompanying the deterioration of lubricants by oxidation is the resultant corrosion of the metal surfaces for which such lubricants are designed and supplied. Once a lubricant has been oxidized to produce viscous sludges and resins, acids develop which are corrosive enough to attack most metals and result in excessive metal wear. Because of the adverse effects of using deteriorated lubricants, the user is constrained to replace the lubricants at more or less frequent intervals.
Newer and larger engines are being made that operate under conditions that create a more severe environment for the lubricants. Petroleum crude oils which were previously suitable for lubricant production are presently unsuitable or at best marginal for such use. Thus at a time when overall lubricant demands are increasing, the amount of suitable lubricant feedstock material is being diminished due to the oxidative stability requirements of newer and larger machinery.
Lubricant base stocks are usually prepared by refining fractions of the atmospheric residium of suitable petroleum crudes. Refining consists of one or more subtractive operations, such as solvent extractions, to remove undesirable constituents such as waxes, resins, and low viscosity index compounds. These subtractive operations characteristically result in very substantial but necessary volume losses. Deep furfural extraction with concomitant high loss, for example, may be needed not only to arrive at a high viscosity index base stock but also to impart the required oxidation stability. Removal of waxes to reduce pour point may be conducted with solvent, or catalytically with a ZSM-5 type catalyst as described in U.S. Pat. No. 3,700,585; or by the sequential use of solvent and catalyst as described in U.S. Pat. No. 3,755,138.
Various antioxidant additives, such as described for example in U.S. Pat. No. 3,399,041 (McCabe), have been developed to improve the oxidative stability of lubricant base stocks. However, such additives are expensive to produce and may present metering and mixing problems when added to lubricants.
Accordingly, it is an object of this invention to provide a method whereby the oxidative stability of lubricant base stocks is improved.
A further object of this invention is to provide a high-yield method of treatment whereby hydrocarbon base stocks of poor or marginal quality may be upgraded in oxidative stability.
Another object of this invention is to provide a method of lubricant treatment whereby the lubricant produced has sufficient oxidative stability to substantially reduce metals corrosion and wear when employed as a lubricant for such metals.
Another object of this invention is to provide a method of upgrading lubricant base stocks to a quality adequate for use in severe service environments.
Other objects and advantages of this invention will become apparent to those skilled in the art upon reading the entire specification including the following detailed description and claims.